1. Field of the Invention
This invention relates to an apparatus for removing unwanted matter such as residue ink from a blanket cylinder in a printing press, and more particularly, to a blanket cylinder cleaning apparatus having a pressure pad capable of pressing a cleaning fabric against the outer peripheral surface of the printing press blanket cylinder to effectively wipe the unwanted matter from the blanket cylinder.
2. Description of the Prior Art
A blanket cylinder in an offset printing press is commonly accompanied by a blanket cylinder cleaning apparatus to wipe unwanted matter such as residual ink and paper fragments from the outer peripheral surface of the blanket cylinder by pressing a cleaning fabric against the rotating blanket cylinder. In general, to heighten the effect of cleaning the blanket cylinder, the blanket cylinder cleaning apparatus has a washer for spraying a washing solution such as an ink solvent or water on the blanket cylinder.
In a blanket cylinder cleaner described in U.S. Pat. No. 4,344,361 to MacPhee et al. (corresponding to Japanese Patent Publication No. HEI 2-6629(B)), a cleaning fabric is brought into press contact with a rotating blanket cylinder to clean the cylindrical surface of the blanket cylinder.
To be more specific, as shown in FIG. 1, the blanket cylinder cleaner of this type comprises a fabric supply roll 4a and a fabric take-up roll 4b so that the cleaning fabric 2 unwound from the supply roll 4a is taken up by the fabric roll 4b. The cleaning fabric 2 traveling between the rolls 4a and 4b comes into contact with the blanket cylinder C while being pressed against the blanket cylinder C by a pressure pad 6. The blanket cylinder cleaner is arranged in parallel to the blanket cylinder C so as to bring the entire length of the cleaner into press contact with the blanket cylinder C as illustrated. The fabric rolls 4a and 4b rotate in the same direction as the blanket cylinder C, so that the contact surfaces of the cleaning fabric 2 and the blanket cylinder C relatively move in opposite directions so as to wipe off residual ink adhering to the blanket cylinder C with the cleaning fabric 2.
The pressure pad disposed in the conventional cleaning apparatus of this type has been formed by curving a rubber plate in the shape of a semi-columnar cylinder or made of a rubber tube (as proposed by Japanese Utility Model Publication No. HEI 4-44370(B)), and retained by a supporting member so as to press the cleaning fabric against the blanket cylinder.
The blanket cylinder cleaner in the afore noted U.S. Pat. No. 4,344,361 is provided on the supporting member for the pressure pad with an air supply path capable of supplying air into the inside space within the pressure pad so as to inflate or deflate the pressure pad for permitting the cleaning fabric to be brought into contact with or separated from the blanket cylinder. The supply of air into the pressure pad brings about a possibility of enhancing the elasticity of the pressure pad. Instead of air, a fluid such as water or oil may be supplied into the pressure pad.
The pressure pad for pressing the cleaning fabric against the blanket cylinder is however required to possess sufficient elasticity and steady shape retention so as to bring the cleaning fabric into stable contact with the blanket cylinder.
Incidentally, the blanket cylinder inevitably has a joint gap extending in the longitudinal direction of the blanket cylinder for drawing a sheet of printing paper in a printing operation. Thus, the blanket cylinder rotating at a high speed generates vibrations and noises when being in contact with the cleaning fabric pressed by the pressure pad to clean the peripheral surface of the blanket cylinder. Accordingly, since the pressure pad cannot withstand the contact stress and vibrations caused by the press contact with the blanket cylinder rotating at a high speed, far from retaining an appropriate shape, the pressure pad, which is merely sustained by air supplied into the inside space thereof, entails problems such as increases in vibrations and noises thus generated and failure to achieve contact of the cleaning fabric with the blanket cylinder. As a result, the performance of removing the unwanted matter such as residual ink from the blanket cylinder and the durability of the pressure pad are remarkably decreased.
Even by using fluid having low viscosity fluid or water in place of the air in the inside space of the pressure pad, the pressure pad entails the same disadvantage as described above. In the case of using water or other fluid, a printing system including the blanket cylinder will suffer a serious disadvantage such that when the pad containing the water is broken due to degradation or other possible causes, the printing system will be adversely effected and printing papers will be stained by the fluid.
As described above, the supplying of air or water into the inside space of the pressure pad produces the effect of somewhat increasing the elasticity of the pressure pad, but never increases the cleaning efficiency and durability of the pressure pad.
The conventional pressure pad which is selectively inflated or deflated by controlling air introduction will be explained in detail with reference to FIG. 2. A blanket cylinder C is wiped up by a cleaning fabric 2 traveling in the direction D2 opposite to the direction Dc in which the cylinder C rotates. A pressure pad 6 is held by a supporting member 8 and has an inside space 6a defined by a wall curved in a semi-circular shape. To press the cleaning fabric 2 against the blanket cylinder C, compressed air is introduced into the inside space 6a in the pressure pad 6 to expand the pressure pad 6.
The rubber pressure pad 6 is expanded and retained in its shape by the pressure of the air. Nevertheless, the shape retention thereof is insufficient, and what is worse, since the pressure pad 6 is fixed at opposite side edges thereof to the supporting member 8 as shown in FIG. 2, it locally protrudes particularly at its central portion thereof and expands unevenly over the entire surface. As a result, uniform cleaning cannot be fulfilled.
Moreover, when the pressure pad 6 presses the cleaning fabric 2 against the blanket cylinder C during the cleaning operation, a tractive force produced by the cleaning fabric 2 traveling in the direction of D2 acts leftwards upon the pressure pad 6 in FIG. 2. Since the elasticity of the air introduced into the inside space of the pressure pad 6 is insufficient to steadily retain the shape thereof, the pressure pad 6 is deformed or collapsed in the direction D2 in which the cleaning fabric 2 is forwarded, as illustrated, consequently causing unevenness in cleaning.
Incidentally, the state of contact of the cleaning fabric 2 with the blanket cylinder C is usually represented by a nip width (contact area) and a nip pressure (contact pressure). When the pressure pad sustained by the internal pressure for air has been in use of a long period of time, it becomes easy expandable and undergoes a change of the nip conditions, possibly resulting in misalignment and aberration in nip conditions.
As noted above, the conventional blanket cleaning device utilizing the air-filled type pressure pad as noted above is disadvantageous in that the pressure pad is insufficient in shape retention and cannot endure prolonged use and hard conditions for stably cleaning the blanket cylinder rotating at a high speed.